hostage (n.)

late 13c., from Old French ostage, hostage "kindness, hospitality; residence, dwelling; rent, tribute; compensation; guarantee, pledge, bail; person given as security or hostage" (11c., Modern French ôtage), which is of uncertain origin. Either from hoste "guest" (see host (n.1)) via notion of "a lodger held by a landlord as security" [Watkins, Barnhart]; or else from Late Latin obsidanus "condition of being held as security," from obses "hostage," from ob- "before" + base of sedere "to sit," with spelling influenced by Latin hostis. [OED, Century Dictionary]. Modern political/terrorism sense is from 1970.